Vacuum pump apparatus



July 22, 1969 M. Doc'roRoFF 3,456,870

VACUUM PUMP APPARATUS Filed March e, 1967 Y 2 sheets-sheet 1 35 aa a4 /3July 2z, 1969 M. Dom-@HOFF 3,456,870 'f VACUUM PUMP APPARATUS FiledMarch 6. 1967 2 Sheets-Sheet 2 lll/Il ltgl lll/Il 13 35 aa @'4- se eral;S {wwf-034:

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United States Patent O 'l 3,456,870 VACUUM PUMP APPARATUS MichaelDoctoroif, 82 Indian Head Road, Framingham, Mass. 01701 Filed Mar. 6,1967, Ser. No. 620,759 Int. Cl. F04 5/44 U.S Cl. 230--108 17 ClaimsABSTRACT F THE DISCLOSURE A vacuum pump apparatus having a rotor withpumping chambers into which a pumping fluid is injected and dischargedby centrifugal force. The pumping chambers are sealed in a fluid bathand periodically register with an inlet port thereby providing a pumpingaction.

This invention relates generally to Vacuum pumps and, more particularly,to a fluid sealed, rotary vacuum pump.

Mechanical vacuum pumps of various types have been developed for use inthe low to medium vacuum range between atmosphere and -2 torr. Thevarious types include piston pumps, bellows pumps, rotary piston pumps,gear pumps, centrifugal pumps, etc. Although such pumps operateeffectively in many vacuum applications, their cost has beenundesireably high primarily because of the close manufacturingtolerances required for establishing suciently tight vacuum sealsbetween the pumps moving parts. Furthermore, because of this tolerancerequirement, the inherent mechanical wear between moving partsmaterially shortens the pumps operating life.

The object of this invention, therefore, is to provide an improvedmechanical vacuum pump which is effective in the low and medium Vacuumranges and which alleviates requirements for close operating tolerancesbetween moving parts thereby both reducing manufacturing costs andextending the useful life of the pump.

One feature of this invention is the provision of a mechanical vacuumpump having a rotor which is closely conned axially by the end walls ofa pump casing and which defines a plurality of radially extending,outwardly opening pumping chambers. The pump casing includes acircumferentially spaced pumping port and fluid inlet port whichsequentially and periodically register with inner portions of thepumping chambers `during each revolution of the rotor and a dischargeport spaced radially outwardly from the fluid inlet and pumping ports.Fluid injected into the pumping chambers through the iluid inlet port isexpelled outwardly by centrifugal force thereby removing the chambersgas content for discharge through the discharge port. The void createdin the pumping chamber behind the expelled lluid produces a pumpingaction on the pumping port upon subsequent registry therewith. Byutilizing the injected fluid as a pumping mechanism, the requirement forclose tolerances between moving mechanical parts is eliminated. Thislessens manufacturing costs by permitting the use of relativelyinexpensive molded parts rather than closely machined metallic parts.

Another feature of this invention is the provision of a vacuum pump ofthe above featured type including a reservoir housing lled with a bodyof sealing fluid under which the iiuid inlet and discharge ports aresubmerged. The pump of this construction possesses an extremely simpleconfiguration requiring a minimum of separate components.

Another feature of this invention is the provision of a vacuum pump ofthe above featured type wherein the pump casing is completely submergedin the body of the sealing fluid and the rotor is rotated in asubstantially horizontal plane by a shaft which passes through the3,456,876 Patented July 22, 1969 ICC' body of sealing uid. In thisarrangement the required number of pump parts is further reduced and thebody of sealing uid provides a fluid seal for the pump casing.

Another feature of this invention is the provision of a vacuum pump ofthe above featured type wherein the radial spacing between the outerperiphery of the rotor and the side w-alls of the pump casing variessubstantially about the circumference of the rotor. The variable spacingproduces distinct operating pressure regions within the pump casingthereby beneficially affecting pump performance.

Another feature of this invention is the provision of a vacuum pump ofthe above featured type wherein the discharge port communicates directlywith a pump casing volume located between the rotor and the casing sidewalls and wherein the spacing between the fluid inlet port and thecasing side wall is greater than the spacing between the pumping portand the casing walls. It has been found that pump performance isoptimized with this particular arrangement of the various ports.

Another feature of this invention is the provision of a vacuum pump ofthe above featured type wherein the rotor is a unitary body having slotswhich form the pumping chambers. The use of a unitary rotor furtherreduces cost of simplifying both manufacturing and assemblyrequirements.

Another feature of this invention is the provision of a vacuum pump ofthe above featured type wherein the rotor possesses between the pumpingchambers solid portions of substantial circumferential width whichcreate with the casing end walls relatively lengthy vacuum seals betweenthe individual pumping chambers thereby irnproving pump performance.

These and other features and objects of the present invention willbecome more apparent upon a perusal of the following specification takenin conjunction with the accompanying drawings wherein:

FIG. 1 is an elevational view partially in cross-section, illustrating apreferred pump embodiment of the in- Vention;

FIG. 2 is a cross-sectional view, partially cut-away, taken along lines2-2 in FIG. l and FIG. 3 is a cross-sectional view taken along lines 3 3in FIG. 2.

Referring now to FIG. 1, there is show nthe reservoir housing 11including the hollow cylinder 12 closed by the circular bottom wall 13and the circular top wall 14. Positioned within the housing 11 is thevacuum pump casing 15 having side walls formed by the hollow cylinder 16and end walls formed by the circular cover plate 17 and the bottom wall13 of the housing 11. The pump casing 15 is secured by cap screws 18which pass through an outwardly projecting ange portion of the coverplate 17 and threadedly engage the bottom wall 13. Mounted on the topwall 14 is the electric motor 19 having the shaft 21 which extendsthrough apertures in the top wall 14 and cover plate 17 and is engagedfor rotation with the rotor 22. The pumping inlet tube 23 is connectedto the pump casing 15 and extends through an opening in the top wall 14.

As shown more clearly in FIGS. 2 and 3, the circumferential periphery ofthe pump rotor 22 is interrupted by a plurality of uniformmly spacedslots which form pumping chambers 24 opening outwardly inot the volumebetween the rotor 22 and the cylindrical side wall 16. The axial lengthof the rotor 22 is substantially equal to the spacing between the pumpsend walls 13 and 17 so as to form relatively gas tight seals therewithbetween the pumping chambers 24. However, satisfactory performance isobtained with clearances between the rotor 22 and the end walls r13and17 in the order of .004-.015

inch. Clearances of this order are substantially greater than thetypical .001 inch and smaller clearances required in conventional vacuumpumps. To further enhance the sealing capability of the closely spacedrotor 22 and side Walls 13 and 17, the circumferential widths of therotor solid portions separating the pumping chambers 24 are preferablyrelatively large as shown in FIG. 2. In this regard it has been founddesirable from standpoints of both performance and production, toutilize a rotor 22 which is a sloltted unitary member and can be easilyproduced by Aconventional molding or casting of plastic or metallicsubstances.

The motor shaft 21 extends through a central opening 25 in the end wall17 and into a central aperture 26 in the rotor 22. Rotational couplingbetween the motor shaft 21 and the rotor 22 is provided by a ridge 27 inthe aperture 26 which engages a longitudinal key slot in the shaft 21.Also located in the pump casing end wall 17 are the inlet pumping port31, the iluid inlet port 32 and the discharge port 33. The inlet pumpingport 31 receives the inlet tube 23 while the fluid inlet port 32 and thedischarge port 33 provide direct communication between the interior ofthe pump casing and the surrounding Volume within the reservoir housing11.

The pumping port 31 and the iluid inlet port 32 are equally spacedradially from the center of the rotor 22 and are so positioned as toperiodically register with the interior portions of the pumping chambers24 during rotation of the rotor 22. Conversely, the discharge port 33 isspaced farther from the rotor center so as to communicate with the openvolume 35 formed by the gap between the rotor periphery and the casingside Wall 16. As shown, the size of this gap varies substantially aboutthe circumference of the rotor because of its eccentricity with thecasing side wall 16. Preferably, the iluid inlet port 32 is sopositioned as to be spaced farther from the casing side wall 16 than isthe inlet pumping port 31.

Prior to operation, the reservoir 11 is lllled with a suitable sealingtluid 38 through an opening 39 in the top wall 14. The sealing fluid 38can be any of a wide variety of fluid substances capable of functioningin the manner described below. However, because extensive lubrication isnot required, water with its desireable low cost and low viscositycharacteristics is uniquely suited for use with vthe device. Examples ofother suitable fluids include mechanical pump oils, diffusion pump oils,mercury, etc. After filling the reservoir 11 with the pumping lluid 38and connecting the pumping tube 23 with a chamber (not shown) |to beevacuated, the electric motor 19 is energized from a conventional powersource (not shown) to produce r0- tation of the shaft 21 and attachedpump rotor 22.

It is difficult to provide from a strictly technical basis a full andexact explanation of the pumping phenomenon which occurs in the pumpcasing 15. Nevertheless, under actual tests, the pump configurationshown in FIGS. 2 and 3 has exhibited remarkable pumping performancecapabilities and although a detailed theoretical explanation of thepumping phenomenon will not be attempted, a rather general andtheoretical explanation of the observed pumping action is presentedbelow.

The revolving rotor 22 throws pumping fluid 38 outwardly from the centerof the casing 17 by centrifugal force, producing a ring of sealing lluidrevolving within the casing 17 and against the side wall 16 at rotorspeed. Because of the eccentricity between the rotor 22 and the casingcylinder 16, the spacing between the fluid ring and the rotor centerwill vary about the circumference of the pump. Thus, the fluid freeVolume in an individual pumping chamber 24 will vary during a rotationalcycle. For example, the fluid free inner volume of the pumping chamber24 is large adjacent the discharge port 33 Where the spacing between therotor 22 and the casing side wall 16 is large but is smaller at aposition diametrically 0pposite thereto where the revolving uid ring isforced into the pumping chamber by the closely adjacent side wall 16. Aseach pumping chamber 24 registers with the iluid inlet port 32 a bead ofpumping lluid 38 is injected from the reservoir 11. Centrifugal forcedrives the bead outwardly creating behind it a void formed by the bead,the walls of the pumping chamber and the casing end walls 13 and 17. Theair ahead of the lluid bead is forced into a relatively high pressureregion existing between the fluid bead and the revolving iluid ring.This pressure region somewhat retards outward movement of the uid beadsuch that before discharge from the pumping chamber it will reach acircumferential position wherein the revolving iluid ring is beingforced into the pumping chamber as a result of the diminished spacingbetween the rotor 22 and the casing side wall 16. At this time theliquid ring will seal the outer opening of the pumping chamber so as tomaintain therein the void created by the injected fluid bead. Uponfurther rotation of the rotor 22 this void will register with thepumping inlet port 31 as the fluid ring is again withdrawing from thepumping chamber. The registry of the void and the inlet port 31 producesa pumping action on the attached pumping inlet line 23, and air enteringthe port 31 will be immediately discharged upon alignment of the chamberwith the fluid inlet port 32 in the manner just described. Air forced bythe lluid bead into the Volume 35 and sealing fluid excess created bythe beads injection are forced by the existing pressures within the pumpcasing 17 outwardly through the discharge port 33 into the fluid body38. The above pumping action occurs in each pumping chamber 24 duringeach revolution thereof with the rotor 22.

In a tested embodiment of the pump shown in FIGS. 2 and 3, thecylindrical casing 16 had an internal diameter of 2%4 inches, the rotor22 had a diameter of 1% inches and an axial length of .575 inch, and theminimum radial spacing between the rotor 22 and the Ycasing side wall 16was about AG inch. This pump was successfully operated at a rotor speedof 5800 revolutions per minute.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventioncan be practiced otherwise than as specifically described.

What is claimed is:

1. A vacuum pump apparatus comprising a pump casing having side wallmeans closed by spaced apart end walls, a rotor adapted for rotationbetween said end walls, drive means adapted to produce rotation of saidrotor, said rotor defining at least one generally radially extendingoutwardly opening pumping chamber, an inlet pumping port in said casingadapted to periodically register with the inner portion of said pumpingchamber during rotation of said rotor, a fluid inlet means adapted toinject fluid through an inlet port into the inner portion of saidpumping chamber, said fluid inlet port and said pumping port beingcircumferentially spaced so as to sequentially register during rotationof said rotor with the inner portion of said pumping chamber, and adischarge port located in said casing and spaced radially outwardly fromsaid inlet pumping port so as to receive fluid discharged outwardly bysaid pumping chamber.

2. A vaccum pump apparatus according to claim 1 wherein the outerperiphery of said rotor possesses a plu rality of slots that define aplurality of generally radially extending outwardly opening pumpingchambers having inner portions adapted to periodically and sequentiallyregister with said inlet pumping port and said iluid inlet port.

3. A vacuum pump apparatus according to claim 2 wherein the rotor solidportions between said slots have a thickness substantially equal to thespacing between said end walls so as to form therewith relatively gastight seals.

4. A vacuum pump apparatus according to claim 3 wherein said tluid inletport is located in one of said end walls and positioned so as toperiodically register with l the inner portions of said pumping chambersduring rotation of said rotor.

5. A vacuum pump apparatus according to claim 4 wherein said drive meanscomprises a shaft extending into said easing and connected for rotationwith said rotor.

6. A vacuum pump apparatus according to claim 5 including a reservoirhousing means adapted to contain a body of sealing iluid and whereinsaid uid inlet port and said discharge port are in iluid communicationconnection with the body of sealing uid.

7. A vacuum pump apparatus according to claim 6 wherein said uid inletport and said discharge port are adapted to be submerged in the body ofsealing Huid.

8. A vacuum pump apparatus according to claim 7 wherein said shaftpasses through the body of sealing uid, and said rotor is adapted forrotation in a substantially horizontal plane.

9. A vacuum pump apparatus according to claim 8 wherein a bottom wall ofsaid reservoir housing forms one of said pump casing end walls, and saidinlet pumping port, said uid inlet port and said discharge port compriseapertures in the opposite pump casing end wall.

10. A vacuum pump apparatus according to claim 6 wherein the radialspacing between the outer periphery of said rotor and said pump casingside wall means varies substantially about the circumference of therotor.

11. A vacuum pump apparatus according to claim 10 wherein said dischargeport directly communicates with a volume located between said rotor andsaid pump casing side wall means.

12. A vacuum pump apparatus according to claim 11 wherein the spacingbetween said fluid inlet port and said casing side wall means is greaterthan the spacing between said inlet pumping port and said casing sidewall means.

13. A vacuum pump apparatus according to claim 12 wherein said casingside wall means comprises a cylinder and the rotational axis of saidrotor is eccentric to said cylinder so as to create the variations insaid radial spacmg.

14. A vacuum pump apparatus according to claim 6 wherein the said rotorsolid portions have substantial circumferential widths so as to providerelatively large circumferential separations between said pumpingchambers.

15. A vacuum pump apparatus according to claim 14 wherein said rotor isa unitary body having said slots which form said pumping chambers.

16. A vacuum pump apparatus comprising a pump casing having side wallsmeans closed by spaced apart end walls, a rotor adapted for rotationbetween said end walls, drive means adapted to produce rotation of saidrotor, said rotor dening at least one generally radially extendingoutwardly opening pumping chamber, an inlet pumping port in said casingadapted for gas communication with the inner portion of said pumpingchamber during rotation of said rotor, a uid inlet port adapted toinject uid into the inner portion of said pumping chamber duringperiodic registration therewith, a discharge port located in said casingand spaced radially outwardly from said inlet pumping port so as toreceive uid discharged outwardly by said pumping chamber, and areservoir housing means adapted t0 contain a body of sealing uid thatinundates said inlet fluid port and said discharge port.

17. A vacuum pump apparatus according to claim 16 wherein said rotor isadapted for rotation in a substantially horizontal plane, and said pumpcasing is adapted to be completely submerged by the body of sealing uid.

References Cited UNITED STATES PATENTS 1,107,999 8/1-914 Petermoller230--108 1,230,216 10/1919 Fisher 230-08 1,457,536 6/1923 Maclean230-108 FOREIGN PATENTS 972,038 10/1950 France HENRY F. RADUAZO, PrimaryExaminer U.S. Cl. X.R. 230-47, 134

